The closing times of fuel injectors are lengthened not only by adhesion forces between the armature and core but also by eddy currents. To reduce the delays, it is known, for example, to select a heavier design for the restoring spring acting upon the armature. To ensure that the opening times of the fuel injector will not be adversely affected by the increased restoring force of the restoring spring, stronger magnetic circuits must be developed which require larger dimensions of the magnetic coils, higher supply voltages, a greater number of turns per unit of length and more expensive magnet materials for their operation.
In addition, to speed up the decay of the residual field, it is known to allow a current to flow through the magnetic coil in the reverse direction once the current pulse energizing the fuel injector has come to an end. However, the construction of appropriate control elements is costly and shortens the closing times to a merely negligible extent.
Another possibility consists in generating one magnetic field for the opening of the fuel injector and a second magnetic field for holding the fuel injector in its open position. The strength of the holding field can then be selected to be so small that the eddy currents are low when the holding field is switched off, thereby allowing the closing time to be shortened.
From German Patent No. DE 23 06 007, an electromagnetically actuable fuel injector for injecting fuel into an internal combustion engine is known where the magnetic coil has three windings which are controlled by three separate switching circuits. The first switching circuit is used for the rapid opening of the fuel injector, the second switching circuit is used to keep the fuel injector open; and the third switching circuit is used to generate a demagnetizing field so as to decay the residual magnetic field for the rapid closing of the fuel injector.
A disadvantage of the fuel injector known from German Patent No. DE 23 06 007, in particular, is the costly manufacture of a system having three switching circuits controlling three windings of the magnetic coil. The increased space required by the switching circuits is an additional disadvantage. An active restoration by a magnetic force component acting in the closing direction does not take place.